E0007: duplicate_signal

E0007 duplicate_signal — two handlers of one cell share a name.

A compile-time error of soma check, the checker of the Soma programming language (soma explain E0007).

The rule

A cell may not have two on handlers with the same name, even when their parameters are identical; Soma does not overload handlers. A call balance(owner) must resolve to exactly one body. Give the second handler its own name (here balance_in_units), or merge the two bodies into one.

A program that triggers it

cell Wallet {
    memory {
        balances: Map<String, Int> [persistent]
    }
    on balance(owner: String) {
        return balances.get(owner) ?? 0
    }
    on balance(owner: String) {
        return (balances.get(owner) ?? 0) / 100
    }
}

What soma check prints:

$ soma check wrong.cell
error: duplicate signal 'balance' in cell 'Wallet'
  --> wrong.cell:8:5
  |
8 |     on balance(owner: String) {
  |     ^
  = code: E0007
✗ 1 error(s), 0 warning(s).

The fix field of soma check --json: Remove the duplicate handler 'on balance()' in cell 'Wallet'.

The fix

On line 8, on balance(owner: String) { becomes on balance_in_units(owner: String) {.

--- wrong.cell
+++ right.cell
@@ -6,5 +6,5 @@
         return balances.get(owner) ?? 0
     }
-    on balance(owner: String) {
+    on balance_in_units(owner: String) {
         return (balances.get(owner) ?? 0) / 100
     }

With the fix, soma check accepts the program:

$ soma check right.cell
✓ All checks passed.